1. Field of the Invention
This invention relates to a rotary magnetic head drum apparatus for use with a helical scan type video tape recorder.
2. Description of the Prior Art
In a helical scan type video tape recorder (hereinafter, simply referred to as a VTR), a rotary magnetic head is generally rotated on the external periphery of a rotary drum at thirty times per second in the case of a thirty frame per second television signal. If the diameter of the rotary drum is 75 mm, then the relative speed of the magnetic tape and the magnetic head is relatively high, typically, approximately 7 meters per second. For this reason, hitting caused at the instant when the rotary magnetic head first contacts or parts from the magnetic tape, gives rise to the creation of an impulse wave on the magnetic tape. The magnetic tape is influenced by this impulse wave so that a so-called impact error is developed in a reproduced output. This results in degradation of, and colour phase irregularities in, the picture reproduced on a screen by the reproduced output.
FIG. 1 and FIGS. 2A and 2B of the accompanying drawings respectively illustrate examples of previously proposed means for reducing the impact error mentioned above.
In the case of FIG. 1, a slant guide 5 is provided on the exit side of a rotary drum 1 of a typical 1.5 head VTR, around which a magnetic tape 3 is wound in an omega shape over substantially 360.degree., so that a damping effect of an air layer which is established between the magnetic tape 3 and the slant guide 5 reduces the impact error.
In the case of FIG. 2A, a stepped guide 4 as shown in FIG. 2B is provided on the exit side of a drum of a two-head type VTR comprising a rotary drum 2 around which a magnetic tape 3 is wound over substantially 180.degree.. By the use of the stepped guide 4, tension is locally applied to the tape 3 so as to reduce the impact error.
Due to considerations of convenience of the loading of the magnetic tape onto the rotary drum, both of the examples described above provide known means for avoiding the impact error, however, at a position spaced apart from the position where the rotary magnetic head actually hits the magnetic tape. As a result, the impact error reducing effect achieved is insufficient, particularly in a multi-head type rotary drum used in a high quality VTR.